Exploration of Ammonia Production in Blue Green Algae By Bioelectrocatalytic Methods

Ammonia is an important compound to many industries around the world.  Most of the fertilizers used by crop growers have ammonia as an essential ingredient.  It can also be useful as a fuel source, offering greater energy density per unit than hydrogen, and greater safety.  Currently, the predominant method for producing ammonia on an industrial scale is by the Haber-Bosch process.  This process uses steam evolution of methane to provide H₂ gas, which is then combined with N₂ gas over an iron catalyst to form NH₃.  This process requires large amounts of energy as well as high temperatures and pressures. 

In this report, an alternative method for ammonia production is explored.  With Anabaena Variabilis, a photosynthetic cyanobacteria, on a carbon electrode, ammonia can be generated at ambient temperatures and pressures at little energy cost, a few tenths of a volt.^1,2  A bioelectrocatalytic device has been constructed by immobilizing whole cell a. variabilis in a Nafion film modified with a trimethyl octadecyl ammonium bromide (TMODA) salt at an electrode surface.³  The ammonium salt enlarges the pore size of the Nafion structure while neutralizing the acidic environment of the polymer, and provides a hospitable matrix for the algae cells. The polymer modified electrode provides the driving force and reductive microenvironment to facilitate production of NH₃ by nitrogenase and nitrate/nitrite reductase enzymes present in a. variabilis.  Ammonia production by cyanobacteria was increased from basal levels of 2.8 ± 0.4 µM produced over a two week period, to 22 ± 8 µM produced in 20 minutes under mild voltage perturbation, a roughly 10⁴ increase in rate. Control of ammonia producing structures (nitrogenase or nitrate/nitrite reductase) can be accomplished by growing the algae with and without fixed sources of nitrogen in the growth media. The addition of nitrates and nitrites to the electrolyte during voltammetric perturbation varies linearly with ammonia increased with substrate.

References:

[1] Johna Leddy and Timothy M. Pashkewitz, Ammonia Production Using Bioelectrocatalytic Devices, US Patent Application 20140011252.

[2] Timothy M. Paschkewitz. Ammonia Production at Ambient Temperature and Pressure: An Electrochemical and Biological Approach. Ph.D. dissertation. University of Iowa, 2012.

[3] Tamar L. Klotzbach; Michelle Watt; Yasmin Ansari; Shelley D. Minteer. Improving the microenvironment for enzyme immobilization at electrodes by hydrophobically modifying chitosan and Nafion polymers.Journal of Membrane Science, 311, 1-2, 20 March 2008, 81-88.